Can't clear the List in DataGridView

foreach (Control ct in cntr.Controls)
           {
               if (ct is TextBox)
               {
                   ((TextBox)ct).Clear();
               }
               else if (ct.HasChildren)
               {
                   ClearFields(ct);
               }
               else if (ct is ComboBox)
               {
                   ((ComboBox)ct).SelectedIndex = -1;
               }
               else if (ct is RichTextBox)
               {
                   ((RichTextBox)ct).Clear();
               }
               else if (ct is DataGridView)
               {
                   ((DataGridView)ct).Rows.Clear();
               }
           }